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Formula: Os
Transition metal, platinum group element
Iridosmine is a variety of osmium rich in iridium (all natural osmium
contains some iridium) (Mindat).
Specific gravity: 22.48 measured for naturally occurring osmium; 22.61 for the chemically pure element at
20oC; osmium is the densest of all the elements (ChC).
Hardness: 7.0 mohs
Streak: Grey
Colour: White
Common impurities: Pt,Rh,Pd
Melting point: 3030oC, osmium has the highest melting point of the
platinum group elements
Boiling point: 5012oC
Abundance in the Earth's crust: 1.5 parts per billion by mass, 0.2 parts per billion by moles, osmium is the
fifth rarest element in the Earth's crust
(ChC).
Abundance in the Solar System: 2 parts per billion by mass, 20 parts per trillion by moles
(ChC).
The most common oxidation state is +4
Environments
Igneous environments
Placer deposits
Osmium occurs with other platinum-group elements and alloys, in
ultramafic rocks and placers derived therefrom (HOM).
An alloy of 90% platinum and 10% osmium is used in surgical implants
such as pacemakers and replacement heart valves
(ChC).
Localities
At Ruby Creek, Surprise Lake, Atlin Mining Division, British Columbia, Canada, osmium is associated with
rutheniridosmine
and osmiridium
(HOM).
In Russia, osmium is found in many localities, including the Gusevogorskii pluton and the Kytlym and Uktus
complexes, Ural Mountains; the Neozhidannyy Creek placers, Tuva; and the Pustaya River placers, Kamchatka Peninsula.
Associated minerals include isoferroplatinum,
cuprorhodsite, malanite,
cuproiridsite,
laurite, erlichmanite,
cooperite, sperrylite,
chalcopyrite and bornite
(HOM).
At Fox Gulch, Salmon River - Red Mountain District, Goodnews Bay, Bethel Census Area, Alaska, USA, osmium is
associated with bowieite, platinum,
iridium–platinum alloys,
laurite and silicate inclusions
(HOM).
Osmium-bearing minerals
Mindat lists only 10 mineral species with essential osmium, but considering the IMA approved formulae, in three
of these species osmium is not essential, so there are only 7 IMA-approved osmium-bearing species.
Osmium-bearing minerals include:
Alloys
rutheniridosmine
Sulphides
erlichmanite
osarsite
Arsenides
omeiite
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